Chemical lasers are devices that derive their population inversions from exothermic chemical reactions, whether directly or indirectly, and include photochemical-induced bond dissociation, radiative recombination of atoms or molecules, and energy transfer processes. In view of their generally efficient conversion of chemical potential into laser radiation, chemical lasers have been sought after for numerous applications in which lightweight, self-contained lasers are utilized.
On the first chemically-pumped electronic transition laser, continuous wave (cw) laser oscillation was achieved using the I*(2P½)−I(2P 3/2) transition via the energy transfer reaction between the oxygen metastable, O2(a1Δ) and a ground state iodine atom, I(2P 3/2). This chemistry forms the basis of the high-powered Chemical Oxygen Iodine Laser (COIL), which operates in the near infrared at 1.315 μm with cw power of up to 40 kW. The COIL uses a heterogeneous mixture of chlorine gas and an aqueous peroxide-based solution to generate the I*(2P½). It is based on the following chemical mechanism,2O2H−+Cl2→2 Cl−+H2O2+O2(a1Δ)   (1)nO2(a1Δ)+I2→O2(X3Σ−)+2 I(n=2−5)   (2)O2(a1Δ)+I→I*+O2(X3Σ−)   (3)I*(2P½)+Hv→I(2P 3/2)+2 hv   (4)The principal limitations of this device are derived from the aqueous (H2O based) chemistry. In general, the use of the aqueous reagents reduces the overall efficiency and increases the complexity of the system because the aqueous peroxide solution is heavy and difficult to engineer and control in a zero gravity environment. In addition, water (H2O) quenches or destroys the I*(2P½) lasing species. Finally, heat generated by reaction (1) is retained in the basic hydrogen peroxide mixture and must be removed to prevent further gas phase H2O generation.
As such, to make the COIL laser viable and robust in all environments (ground, air and space), extensive engineering is required to accommodate the aqueous chemistry. One approach to mitigate these drawbacks was the all gas phase laser system described in U.S. Pat. No. 6,459,717 hereby incorporated by reference. This cw subsonic all gas phase iodine laser (AGIL) eliminated the water-based chemistry and its attendant problems.
The subsonic AGIL is a device in which the energy required for laser operation is achieved through the transformation of the solely gas phase chemical reagents, NF3 (nitrogen trifluoride), DCl (deuterium chloride) HI (hydrogen iodide) and HN3 (hydrogen azide) into I*(2P½) laser radiation at 1.315 μm. Helium is also used, but its role is limited to a buffer or carrier gas for these reagents. The chemical generation of I*(2P½) lasing is based on a sequential process in which Cl and I atoms are produced,F+DCl→DF+Cl,   (5)Cl+HI→HCl+I(2P 3/2)   (6)followed by NCl (a1Δ) production,Cl+HN3→HCl+N3   (7)Cl+N3→NCl(a1Δ)+N2(X1Σ)   (8)and finally the energy transfer reaction between NCl (a1Δ) and I(2P 3/2) to generate I*(2P½):NCl (a1Δ)+I(2P 3/2)→NCl (X3Σ)+I*(2P½)   (9)I*(2P½)+hv→I(2P 3/2)+nhv (1.315 μm laser radiation)   (10)
The demonstration of I*(2P½)−I(2P 3/2) laser action using this mode and chemistry was performed in a transverse subsonic flow reactor. The essential features of this apparatus included a device for fluorine (F) atom production. The device can be an electrical discharge (DC), RF or microwave radiation, or chemical combustion. Fluorine atoms were generated using a 10 kW DC discharge of NF3 in helium. The pressure in the system was regulated by flowing N2 1.5 meters downstream of the reactor cavity through a 3-cm choke orifice. Downstream of the fluorine atom injection point were nozzles or injectors for the insertion of DCl, HI and HN3 into the flow stream.